In personal and commercial watercraft, such as engine-driven fishing boats and speedboats, propulsion systems are often used in which a drive engine of the watercraft is arranged inside the watercraft and is actively connected, via a drive unit in the area of the watercraft's hull, to one or more propellers on the outside of the watercraft's hull. The drive unit typically passes through an opening in the hull or rear transom of the watercraft's hull, and usually includes an upper housing section or gear and clutch housing disposed inside the hull and having a drive shaft connected to an output shaft of the engine, and a lower housing section or underwater housing disposed outside the hull and having one or more output shafts connected to one or more propellers that rotate to drive the watercraft through the water. To avoid having the watercraft take on water through the opening in the hull, the drive unit must be secured within the opening with an arrangement that provides a sufficiently water-tight seal to prevent leakage when the watercraft is disposed and operated in the water.
One example of a known sealing arrangement is provided in U.S. Pat. No. 7,182,657, issued Feb. 27, 2007, to Mansson, which discloses a mounting arrangement wherein a boat hull is formed with a vertical well having an internal flange. The boat hull is used with a drive unit having a vertical drive shaft with an underwater housing connected to an upper gear housing, with the upper gear housing having a horizontal drive shaft for connection to an engine. A mounting plate of a drive unit and a screw-down plate are fastened to opposite sides of the internal flange, with compressible rings between surfaces of the mounting plate and the flange and between surfaces of the screw-down plate and the flange. The rings dampen vibrations from the drive to the hull. The propeller forces are transmitted via the mounting plate and the screw-down plate to the flange and the well and, thus, to the boat hull.
During operation, the watercraft may encounter submerged objects that impact the underwater housing of the drive unit. If the impact force is great enough, the object can damage the drive unit and the boat hull. To minimize the damage and cost to fix or replace damaged components, drive units have been designed so that particular components yield to allow the underwater housing to break away from the remainder of the drive unit and boat hull without causing additional damage. One example of a known of breakaway arrangement shown in U.S. Pat. No. 2,681,029, issued May 5, 1950, to Canozzi, which discloses a drive unit with a steering section having an upper section and a lower section connected by a pivot pin and a sheer pin. The upper section has an upper vertical shaft and the lower section has a lower vertical shaft. At the juncture of the upper and lower sections, companion chocolate elements are secured respectively to adjacent ends of the vertical shafts. The clutch elements are normally engaged for transmission of power between the vertical shafts. When the sheer pin is broken upon impact of the lower section with an object, the lower section swings about the axis of the pivot pin to minimize damage to the drive unit and boat hull, and the clutch elements and, correspondingly the vertical shafts, are separated to prevent bending or breaking of the vertical shafts.
The breakaway arrangement of the Canozzi patent may be effective in reducing damage to the drive unit with the boat hull in impact situations, but opportunities still exist for further improvements to underwater housing breakaway designs. In addition to damage to the drive unit and the boat hull, the potential exists for oil to leak into the water when the underwater housing detaches. Passages are provided for oil to flow from the upper housing section to the underwater section for lubrication of the gear case and shafts disposed therein. When the underwater section breaks away, oil may flow from the passages into the water. In view of this, a need exists for sealing the passages to prevent leakage of oil when the underwater section becomes detached.